1. Field of the Invention
The present invention relates to an axial-flow turbine such as a steam turbine and a gas turbine. More particularly, the invention relates to an axial-flow turbine having an extraction structure for extracting a part of a working fluid.
2. Description of the Related Art
An axial-flow turbine is axially provided with a plurality of stages composed of stationary blades and buckets. In operation, a working fluid in such an axial-flow turbine may be extracted between stages for use as a heat source or for use to drive a rotating machine.
For example, with steam turbines, steam is extracted between stages and then led to a feedwater heater or deaerator. Then, this steam goes out a steam turbine outlet and is subjected to heat exchange with water which is in a liquid phase formed by condensing by using a steam condenser. This process raises the temperature of water before the water is returned to a heater such as a boiler and a nuclear reactor, thus improving power generation efficiency.
There are steam turbines of combined heat and mechanical power cogeneration type or combined heat and electric power cogeneration type. Such steam turbines aim at driving an industrial rotating machine such as a pump and driving a generator and at the same time providing high-temperature and high-pressure steam as a heat source. During operation of these steam turbines, it is necessary to extract steam as a heat source from between stages.
A typical axial-flow turbine having such an extraction structure is provided with a circular-shaped extraction chamber disposed on the outer circumference of a turbine blade chamber in which steam flows. That is, the extraction chamber circumferentially extends around the turbine blade chamber. This extraction chamber and the turbine blade chamber in which steam flows are connected with each other through a slit-shaped extraction opening circumferentially formed toward an outer wall of the turbine blade chamber. A part of the working fluid in the turbine blade chamber is extracted into the extraction chamber through the extraction opening, and then transmitted to a predetermined place via an extraction pipe connected with the extraction chamber (refer to JP-2-241904-A).